This invention relates to radon extraction solvents. Typically, low molecular weight (LMW) organic solvents may be added to conventional liquid scintillation counting (LSC) solutions which have poor or suboptimal abilities to extract radon gas (.sup.222 Rn) from charcoal thereby producing LSC solutions which have optimal abilities to extract .sup.222 Rn from charcoal for measurement of the radiation from .sup.222 Rn and its radioactive daughter products. The invention also relates to the ability of these same solvents when added directly to charcoal to efficiently displace radon from the charcoal and into the gas and/or solvent phases which may be in close proximity to the charcoal. Many methods have been described for the measurement of .sup.222 Rn in air. Several methods rely upon the ability of activated charcoal to adsorb and retain .sup.222 Rn gas from the air. Subsequently, the radioactivity in the charcoal may be measured by direct gamma counting of the charcoal or alternatively by liberating the .sup.222 Rn gas from the charcoal within a closed system for radioactive measurement. With the latter method, for high measurement sensitivity and accuracy it is important that .sup.222 Rn liberation is efficient and reproducible. Only one previous study (Pritchard and Marien, Anal. Chem. 1983, 55, 155-157) has reported a method for liberation of .sup.222 Rn from charcoal into liquid scintillation solutions for radioactive counting. Using gamma counting of the original charcoal and of the separate solvent extract, the above study showed that after submerging granular charcoal in pure toluene for at least two hours and then removing the toluene, almost all of the radon could be accounted for in the toluene. However, quantitative solvent extraction or even high efficiency radioactive counting of radon was not demonstrated when charcoal remained mixed with the toluene (or any other solvents) or when the toluene contained dissolved fluors necessary for liquid scintillation counting. Pritchard and Marien reported that they obtained reproducible but not necessarily quantitative extraction of .sup.222 Rn comparing the (cpm) counts per minute data among multiple LSC vials having "2 g carbon residing on the bottom of the vial" containing a toluene liquid scintillation solution with unspecified fluors. It was separately demonstrated by Perlman that warming a charcoal sample which is either submerged or placed directly above an aromatic solvent based liquid scintillator (containing toluene or xylene for example), accelerates the displacement of .sup.222 Rn from the charcoal into the liquid scintillator.
The above prior art methods using toluene or other monocyclic aromatic solvents based liquid scintillators for extracting and counting radon in free granular charcoal suffer from one or more disadvantages including sub-optimal radon extraction efficiency in counting dry and especially moist (water-containing) charcoal samples, toxicity of the toluene solvent and vapor, and inconvenience and costs involved with incubation, or in the handling, loading, and disposal of the toxid liquid scintillator and the charcoal sample.
One object of the present invention is to provide a liquid scintillator which exhibits improved radon extraction efficiency in counting both dry and moist charcoal samples.
Another object of the invention is to provide a liquid scintillator which is non-toxic and is therefore safe and convenient to use, handle and to later recycle or discard.
A further object of this invention is to provide inexpensive solvents which are compatible with liquid scintillator solutions and which can be applied directly to charcoal to efficiently and rapidly displace the radon contained within the charcoal.